1. Field of the Invention
The present invention relates to a cover structure for exhaust manifold inlet ducts of an engine for a vehicle.
2. Description of the Prior Art
Generation of superheat as well as of a large sound can be seen typically in an exhaust manifold unit in an engine mounted on a vehicle when actuating the engine. In great majority of cases, a cover unit is installed around the manifold for the purpose of shielding both the sound and the heat. There is illustrated one example of such installation in FIG. 5 in association with the prior art. FIG. 5 is a schematic view in side elevation. A plurality of exhaust manifold inlet ducts are laterally aligned along the side part of a cylinder head 6; and the proximal parts thereof are formed integrally with flanges 4. Flanges 4 are fixed to cylinder head 6 by fixing means such as bolts or the like, thus securing the manifold inlet ducts thereto. The foregoing sound-and-heat shielding cover unit is, as in the prior art depicted in FIG. 5, composed of an upper cover 2 and a lower cover 3 which are fixed to a boss provided on a manifold face. In some of other conventional examples, the cover unit is secured to the cylinder head. According to the present invention, however, the construction is based on such a premise that the cover unit is, as depicted in FIG. 5, fitted to the manifold itself.
Based on the structure of the prior art described above, covers 2 and 3 may be installed before or after mounting manifold 1 to cylinder head 6. With a view to obtaining good workability, however, the installation thereof is effected preferably by fastening flange 4 to cylinder head 6 with the bolt generally after fitting covers 2 and 3 to exhaust manifold 1.
FIG. 6 is a view showing in detail a part A of FIG. 5. FIG. 7 is a sectional view taken substantially along the line I--I of FIG. 6. As illustrated in FIGS. 6 and 7, however, where lower cover 3 is, as in the conventional example, fitted to exhaust manifold 1, a spacing between a face 7 of manifold 1 and lower cover 3 has to be restrictively set to, e.g., a in terms of obtaining the sound-and-heat shielding effects. A bolt 5 position in which flange 4 is attached to cylinder head 6 is in itself limitative in terms of installing strength and minimum expansion of flange 4. Consequently, as will be seen in FIG. 7, lower cover 3 tends to, as is often the case, be superposed on bolt 5 when observing flange 4 from the manifold tube; or alternatively, lower cover 3 is disposed in close proximity to bolt 5.
A problem incidental to such an arrangement is that a tool for turning bolt 5 can not be inserted when fitting flange 4 to cylinder head 6 after previously mounting lower cover 3 on exhaust manifold 1. When upper cover 2 is, as shown in FIG. 5, attached beforehand to manifold 1, the tool is never inserted and therefore the fixation can not be effected, unless the bolt of flange 4 is positioned outwardly of upper cover 2. This arrangement does not fall within the scope of the invention.
Lower case 3 is in some cases attached to the underside of manifold 1. After securing manifold 1 to cylinder head 6, the installation thereof entails some difficulty. This is disadvantageous in terms of a working efficiency.
Accordingly, in an exhaust manifold cover unit arranged such that a cover unit for shielding both a sound and heat is attached to a boss provided on an outer periphery of an exhaust manifold of such a type that a flange provided at the proximal part thereof is fastened to a cylinder head with a bolt, it is a primary object of the present invention to provide a cover structure characterized in that a bolt fastening tool can be inserted by causing deformation in a portion on which the cover unit projects in a direction of its tabular width with respect to a bolt for fixing the flange or in the vicinity thereof.